alias-imports

Create bare aliases in the imports map in package.json.

Features

• Supports both ESM import and CommonJS require()
• Subpath patterns support
• Conditions support
• Overwrite import/require()s in dependencies

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Install

npm i -D alias-imports

Usage

Declare aliases in the imports map in package.json:

{
    "imports": {
        // Aliases
        "lodash": "./custom-lodash.js"
    }
}

Then, run your script with the alias-imports loader:

node --loader alias-imports ./file.js

Whenever lodash is imported, ./custom-lodash.js will be loaded.

Subpath patterns

Like Node.js, alias-imports supports subpath patterns.

With this configuration, all lodash/* imports will be aliased to ./custom-lodash/*:

{
    "imports": {
        "lodash/*": "./custom-lodash/*"
    }
}

Conditions

Like Node.js, alias-imports supports conditions.

With this configuration, lodash will be aliased to ./custom-lodash.js by default. But when --conditions underscore is passed in, it will resolve to underscore instead:

{
    "imports": {
        "lodash": {
            "underscore": "underscore",
            "default": "./custom-lodash.js"
        }
    }
}

Pass in a condition:

node --loader alias-imports --conditions underscore ./file.js

Examples

Toggle between Webpack 4 & 5

package.json

{
    // Setup imports to load webpack4 by default
    // and webpack 5 when the webpack5 condition is specified
    "imports": {
        "webpack": {
            "webpack5": "webpack5",
            "default": "webpack4"
        },

        // This entry maps webpack subpaths to webpack4 or webpack5
        "webpack/*": {
            "webpack5": "webpack5/*",
            "default": "webpack4/*"
        }
    },

    // Install Webpack 4 & 5 to webpack4 & webpack5 respectively
    "devDependencies": {
        "webpack4": "npm:webpack@4.42.0",
        "webpack5": "npm:webpack@5.10.1"
    }
}

Load Webpack 4 (default)

node --loader alias-imports ./file.js

Load Webpack 5

Specify the webpack5 condition via the --conditions, -C flag.

node --loader alias-imports -C webpack5 ./file.js

API

Loader

Pass in alias-import/loader to --loader to load the import hook. This will only add alias support to ESM imports.

node --loader alias-imports/loader ./file.js

Require hook

Pass in alias-import/require to --require to load the require hook. This will only add alias support to require() calls.

node --require alias-import/require ./file.js

Both

Passing in alias-imports loads both the loader and the require hook:

node --loader alias-imports ./file.js

Debugging

Set the DEBUG_ALIAS_IMPORTS environment variable to see which imports aliases are being resolved by whom.

DEBUG_ALIAS_IMPORTS=1 node --loader alias-imports ./file.js

Dependencies

resolve-pkg-maps

Used to resolve imports in package.json.

FAQ

How is it different from native imports?

• Native aliases in imports must be prefixed with #, whereas aliases with alias-imports don't.

• Because this loader allows you to create unprefixed aliases, they can be used to overwrite import paths (e.g. lodash can point to underscore).

• Affects dependency packages as well, not just the current package

When should I use this instead of native imports?

In general, you should use native imports when possible. If you're creating a new alias, prefer to use the # prefix.

However, if you're trying to overwrite an import path in a dependency package (e.g. lodash to underscore), you can use this package to achieve that.

Can I use this in published packages?

Published packages should not use this because it relies on the consumer to start the Node.js process with the alias-imports loader.

However, it can be used in application codebases to overwrite import paths in dependencies.